I mean, there are absolutely tons of diets and eating patterns that absolutely will harm the person eating them...
... And if you are regularly encouraging or induldging in that kind of diet among impressionable people, like children, that may transfer to them as normal/acceptable.
Also I guess if you are cooking/eating something that has particularly aerosolized ingredients or elements that other people are allergic to or just find incredibly repulsive, you might cause other people to vomit or have an allergic reaction.
My mom had the same rule about milk. She said if you were running a fever, the milk would "curdle in your stomach" and make you nauseous. Your stomach is acidic. Milk always curdles in your stomach.
Asked my mom about this a few years back because she had the same rule. Turned out, she knew it was mostly bs, but she didnt want to deal with kids puking up curdled milk because it grossed her out, and apparently we had a harder time puking it up so we were more upset.
And honestly, i dont blame her. Depending on the year, she could have had 5 kids in the house all sick to some degree. If it took telling us milk would make us sicker to help ease that stress, I agree with it.
I mean, I've never eaten any cereal with OJ instead of milk, but it seems like it could work with a cereal + OJ combination that isn't too overpowerfully sweet, or just a really strange combo.
Like... Lucky Charms + OJ... seems like it would be weird.
But... OJ + some kind of bran flake based cereal? That... might actually be better than milk, imo.
Now I want to try this haha.
I've always been the kind of person that'll try basically any kind of food at least once.